To get the text entered in the textbox, use the following code
string text = ((TextBox)(GridView1.Rows[e.RowIndex].FindControl("TextBox1"))).TextThe code is used to search for the control in the current row(the row being updated), and getting its text property.
GridView1 is the ID of the gridview
TextBox1 is the id of the TextBox inside the gridview
Thanks